1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD), and more particularly, to an LCD which allows a common electrode voltage swinging depending on a gate off voltage of a display part to be fed-back through a feed-back circuit and to be held at a constant level, thus stabilizing the common electrode voltage and the gate off voltage coupled to a capacitance component, thereby preventing a picture displayed on the LCD panel from being divided into blocks.
2. Description of the Related Art
Generally, an LCD is a mostly used type of flat panel display. Especially, the small size, lighter weight and lower power consumption render the LCD to replace a traditional cathode ray tube (CRT).
The LCD is currently used as a monitor for a portable computer and largely includes an optical module, a display part and a receiving container for containing and fixing these elements.
The display part includes an LCD panel, at least one printed circuit board (PCB) and a tape carrier package (TCP) for physically and electrically connecting the LCD panel and the PCB. The LCD panel includes a TFT substrate, a color filter substrate attached to the TFT substrate, and a liquid crystal layer interposed between the TFT substrate and the color filter substrate. The PCB includes several integrated circuits mounted thereon and interconnection lines for signal transmission. The TCP has a drive integrated circuit (IC) mounted therein.
Technologies in the above constituted display part are being variously developed in order to obtain a large size LCD panel and decrease the volume occupied by the PCB. As one of such technologies, there was filed an application related to an LCD not having the gate PCB in Korean Patent Office by the present assignee as a Korean Patent Application No. 1999-13650.
In this application, a gate drive IC is mounted on the flexible circuit and plural flexible circuits are physically and electrically connected to the TFT substrate with being apart by a constant interval from each other. Here, the interconnection lines for transmitting gate on/off voltages and plural control signals into respective drive ICs are designed to go via an edge of the TFT substrate, and length, area and thickness thereof are designed in such a degree that the signals are not distorted upon considering the resistance of the interconnection lines.
However, when manufacturing the display part of LCDs, especially, the interconnection line which goes via the TFT substrate and the flexible circuit comes to have different resistances depending on a position where the interconnection line arrives at the flexible circuit. Also, the interconnection line is coupled with elements including adjacent interconnection lines to have a capacitance. Accordingly, the gate on and off signals transmitted through the interconnection lines have delay characteristics due to the resistance and capacitance and are input into every gate drive integrated circuit with different amplitudes. This phenomenon is especially highlighted in a case of the gate off voltage.
The gate on/off voltages applied through the interconnection lines does not greatly affect on the common electrode voltage when the display part is driven in a dot inversion method. This is because in a general dot inversion pattern, a large variation of current in the gate off line or common electrode does not occur due to the current compensation effect between adjacent pixels.
However, in a vertical stripe pattern in which a black line and a white line are alternatively displayed between vertical lines which are adjacent in a horizontal direction, such the current compensation effect is minimized.
So, an alternating current coupled with the data line affects on the gate off line and the common electrode, which causes the swing of the gate off voltage and the common electrode voltage.
Finally, due to the resistance difference caused by the length difference of the interconnection lines connected to the gate off line, gate signal has different delay characteristics. Especially, since the gate off voltage is not compensated in the case of the stripe pattern, the gate off voltage swings depending on the swing of the common electrode voltage, so that the common electrode voltage is instabilized. Accordingly, there appears a block phenomenon in which a dim brightness difference is generated at the boundaries of the display region which are divided by separate gate drive ICs.
It is an object of the present invention to stabilize the gate off voltage applied to an LCD panel of a display part by feeding-back the common electrode voltage and thereby prevent the display region of the display part from being made in a block every gate drive IC.
To accomplish the above object, there is provided a liquid crystal display comprising: an optical module for providing a light necessary to form an image; a display part for displaying the image by controlling a transmittance amount of the light provided from the optical module; and a receiving part for receiving and fixing the optical module and the display part.
In the above LCD, the display part comprises: an LCD panel; a PCB for providing a data signal, a gate on/off signal, a common electrode voltage and first plural control signals to operate the LCD panel; a source signal converting part for generating a source signal with the data signal and a second control signal which is contained in the first plural control signals and applying the source signal to the LCD panel; a gate signal converting part for generating the gate on signal and gate off signal with the gate on/off signal and a third control signal contained in the first plural control signals and applying the gate on signal and gate off signal to the LCD panel; and a gate voltage stabilizing part for detecting the common electrode voltage from at least one position, controlling the common electrode voltage which is output when feeding-back the detected common electrode voltage so as to maintain an amplitude of the gate off voltage at a constant level.
In the above LCD, the gate voltage stabilizing part includes: a first feed-back voltage detecting section for detecting a first feed-back voltage from at least one position to detect the common electrode voltage of the LCD panel; a reference voltage applying section for controlling a static voltage into a predetermined voltage level to input the controlled predetermined voltage level as a reference voltage; a comparator for comparing the first feed-back voltage with the reference voltage to output a result obtained from the comparing; and an output section for dividing the result output from the comparator into at least two voltages having different voltage levels from each other to output the divided voltages as the common voltage of the LCD panel.
Preferably, the comparator includes a loop in which an output is mixed with the first feed-back voltage and then is fed-back to the comparator such that the loop stabilizes an output of the comparator when the first feed-back voltage detecting section is opened.
Preferably, the common electrode voltage is detected at a gate side or a source side.